DE2341356A1 - STABILIZED ESTER IMPREGNANT - Google Patents

Description

Stabilized ester impregnation agent

The present invention relates to a stabilized liquid ester impregnant for electrical equipment, and in particular an improved stabilized aromatic ester impregnant » which is particularly suitable for use in electrical capacitors. The invention also relates to Capacitors stabilized with the inventive liquid ester impregnation agents are impregnated as well as a Method of impregnation.

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The dielectric liquid impregnating agent for use in an electrical device of the present invention comprises one liquid aromatic ester to which an epoxy material has been added which is associated with detrimental impurities in Electrical apparatus that are present or generated during their operation can react to the breakdown of the aromatic Avoid Esters.

The aromatic ester can advantageously be a derivative of phthalic acid and for the purposes of the present invention the preferred ester is the reaction product of phthalic acid with 2-ethylhexyl alcohol, which is called di (2-ethylhexyl) phthalate or known simply as dipetyl phthalate - hereinafter referred to as DOP for short.

AC tests on capacitors have shown that DOP can be used as an impregnating agent for high-voltage AC capacitors is not suitable, although it has certain advantageous properties, such as capacitor compatibility, high dielectric constant and biodegradability. These good properties are, however, due to the instability under high electrical loads and the resulting short lifespan. An indication of the short life in a capacitor is a rapidly increasing or high loss or power factor. The power factor, which is a measure of electrical power Loss in a capacitor is generally a critical issue in high voltage AC power capacitors. The electrical instability results in early breakdown or failure and this is critical to Long life capacitors, such as the current chlorinated diphenyl impregnated power capacitors.

Stabilization of the impregnating agent usually includes the addition of small amounts of another material to the impregnation agent, which improve the impregnation agent, by removing the impurities that are present in capacitors or that are generated there and that prevent degradation

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Causes, neutralize. Usually the impregnant to be improved is already a good and effective capacitor impregnant and the stabilizer additive creates a gradual improvement. DOP is a liquid material that is used in its use as an impregnation device in capacitors exposed to elevated temperatures and high voltage loads shows a rapid increase in the power factor and accordingly quickly leads to failure of the capacitor. First Line for these reasons is the development of DOP as a practical one and commercially recognized impregnant for an electrical capacitor were omitted.

However, it has been recognized in the invention that DOP can be effectively stabilized so that it can be used as the sole or primary impregnating agent can be used in an AC capacitor and under high voltage loads. In detail it has been found that epoxides, formerly only considered suitable for removing chlorine or hydrogen chloride can also work in other ways, so that they are DOP .in stabilize a condenser in which hydrogen chloride or chlorine are not normally present in the materials or are generated from them.

The invention is described below with reference to the drawing explained in more detail. Show in detail:

Figure 1 shows an exemplary capacitor winding in which paper is used as the dielectric,

Figure 2 shows a complete capacitor in the form of a sealed one Container containing the roll of Figure 1,

FIG. 3 shows a cross section of part of a capacitor winding in which a film made of a synthetic resin is used as the dielectric is used,

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Figure 4 is a cross-section of part of a capacitor winding in which both paper and a film made of a synthetic Resin can be used as a dielectric,

Figure 5 is a cross-sectional view of a portion of a capacitor coil having a synthetic resin film in a another dielectric arrangement is used in a capacitor, and

FIG. 6 shows a greatly reduced illustration of an example of a power capacitor which contains a multiplicity of windings, as it is commonly used as a large phase shifter, high frequency capacitor or for induction heating will.

DOP is a material that acts as a plasticizer for synthetic plastics is known and which can be purchased from a number of manufacturers, so under the name "Flexol" from - Union Carbide Company. A description of DOP as a plasticizer is found in Arthur K. Doolittle's publication "Die Technology of solvents and plasticizers "under the heading" Properties of individual plasticizers "on the pages to find 964, published in 1954 by the Union Carbide'Company became. In addition, a more detailed description of this product is in US Pat. No. 1-923,938 contain. Typical properties of this product are in the. Table 1 below.

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Table 1 Typical properties of the liquid DOP

Di (2-ethylhexyl) phthalate C ₂₂₄ H-, g 0 ^, molecular weight = 391, density at 25 ° C 0.987 g / cm ⁵
Refractive index N 1.4859

Boiling point 229 ^° C. at 5 mm Hg

Pour point -55 ° C

Dielectric constant (DK) 5.24 at 25 C % loss factor 7.7 %, 8.5 % at 100 ⁰ C and 100 Hz,

measured in about 200 l (equivalent to 55 US gallon) barrels

Viscosity 30 es at 38 ⁰ C (corresponding to 100 ° F)

4.2 it at 99 ⁰ C (corresponding to 210 ⁰ F)

In the context of the present invention, DOP is the only impregnating agent Has been used in capacitors that are either paper only or synthetic / resin only or both as dielectric Materials included.

A preferred embodiment of the capacitor according to the invention includes one or more capacitor coils contained fairly securely in a container that carries a liquid impregnant is filled and sealed. A capacitor coil comprises alternating strips of dielectric and electrode material in various layered arrangements or structures can be united, as z. As described in U.S. Patent 3,363,156.

In Figure 1 is an exemplary capacitor winding 10 with a pair of electrode foils 11 and 12 and paper strips 13 and 14 as Dielectric shown. The electrode foils 11 and 12 can also be designed as metal coatings on the paper strips 13 and 14 be or on separate and additional dielectric strips of various materials including paper

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and plastics. Suitable electrical conductors or taps 15 and 16 are used to connect the electrode foils 11 and 12 to suitable capacitor connections 18 and 19. Of the Roll 10 is arranged in the container 17 of Figure 2 and after suitable drying and evacuation of the container this is with filled with a liquid impregnating agent and sealed. The connections 18 and 19 of the container are with the taps 15 and l6 of the coil 10 connected.

Each dielectric paper strip 13 and 14 can be through a Variety of paper strips can be replaced in order to obtain a thicker dielectric or to take advantage of the electrical benefit of using it to have a variety of strips. Each strip 13 and 14 can also be replaced by one or more strips 20 and 21 of synthetic Resin can be replaced, as shown in Figure 3, or with a mixed dielectric from a strip of paper and a resin strip 20 as shown in Figs. Other typical constructions and embodiments and their Descriptions are contained in the aforementioned U.S. Patent 3,363.

In these typical embodiments, the dielectric liquid impregnating agents leave essentially all of the crevices, pores and spaces in and between the dielectric strips 13 and 14 to penetrate, to penetrate and fill them. This type of impregnation considered to be essentially complete Impregnation is necessary to prevent damaging corona discharges from occurring in AC capacitors reduce their rated or application voltage and cause arcing to avoid. The impregnation agent located in the electric field between the electrodes is of high electrical power Subject to stresses, corona discharges and increased and changing temperatures and other damaging environmental conditions. However, it is believed that these conditions z. B. in power capacitors no failure of the capacitor during cause a service life of 10 to 20 years.

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Accordingly, great care has been taken in the field of capacitors, high purity and compatible materials such as paper and chlorinated diphenyl and it will be a great effort made to gases and water vapor by high temperature drying and evacuate to remove. Impurities present in the materials and structure of a capacitor Are gases, water vapor, and solid impurities, such as chemical — elements and compounds — found in other materials are present, such as B. in paper or in polypropylene film. These chemical elements and compounds can be of foreign nature or they can be used in the manufacture of the other materials and have entered them for this reason. One source of contaminants in the condenser is the catalyst used in the manufacture of polypropylene. A typical catalyst can introduce contaminants in the form of salts of aluminum and titanium. Such impurities can be released from the impregnation agent. So is a chlorinated diphenyl impregnant Solvent that dissolves and transfers impurities and leaches impurities from the dielectric that are necessary for the capacitor are harmful. These impurities react in an unfavorable way with the impregnating agent or combine in another way to react with the impregnant, resulting in degradation, which in a capacitor is first by the Increase in the power factor is noticed.

in

The elevated temperatures at a / operating condenser and the small electrical and corona discharges that occur activate the impurities with subsequent Deterioration of the capacitor; The main elements which are known to cause an earlier capacitor failure are hydrogen and chlorine, which, with the formation of e.g. B. of hydrogen chloride react with each other. Chlorine has heretofore been used as one in capacitor impregnants or an undesirable element in other capacitor materials. Unfortunately it is

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for other reasons as a critical ingredient in considerable amounts in the best available impregnants for change current capacitors, e.g. B. polychlorinated diphenyl remained. For these reasons, there are many additives for chlorinated diphenyl impregnants have been suggested to serve to remove HCl, chlorine, or hydrogen and so be effective and extend the life of the capacitors. These additives include tin tetraphenyl, anthraquinone and epoxies.

As noted, previous efforts were made to impregnate DOP of AC capacitors, thereby preventing those impregnated with DOP AC capacitors exhibited a high power factor and rapid shifting. Since DOP did not contain any known chlorine components, there was no compelling reason to use the listed ones Additives. Tests on DOP-impregnated AC capacitors that were exposed to high voltage loads, such as those described in connection with Figures 1 and 2, showed initially quite good electrical results. In accelerated endurance tests at elevated temperatures, however, occurred in increasing Mass inadequate capacitor failures, primarily due to increasing power factors and subsequent electrical Off £ _all were displayed. The investigations were with repeats the capacitor of Figures 3 and 4, which differs from the capacitor of Figure 1 in that a film of synthetic resin replaced the paper strips 13 and 14 of FIG or used together with them. Failures similar to those of the paper capacitors occurred. An investigation revealed neither the presence of HCl nor chlorine in both cases, as in capacitors impregnated with chlorinated diphenyl would have been expected.

It was surprisingly found that the addition of an epoxy compound to the DOP, the capacitor impregnated with DOP effectively stabilized against an earlier failure and only for a short period of use. A repetition of the above and other suitable

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- «Ta -

Further tests using an epoxy showed a large reduction in failures, as shown in the following examples. In these examples, DOP was purified by a column filtration process using alumina or Fuller's earth as the filter material. The impregnation process was generally carried out in the manner described in US Pat. No. 3,363,156, including drying the capacitors by heating them for several hours at elevated temperatures, such as above 100 ° C and usually below 125 ° C. During this cycle the capacitors were under a vacuum of less than 200 liters of mercury. After impregnation with DOP, which at about 70 - was held 8O ⁰ C, you wrote the capacitors, and gave them drink in the heat for several hours, for. B. 4-16 hours, at about 100 ^° C. The specified heat soaking time does not include the time required for the condenser to reach the desired temperature and the time it takes to cool down to room temperature. The times given are the times at the stated temperature.

example 1

Two groups of capacitors of 10 pieces each, as described with reference to FIGS. 1 and 2, were assembled. The dielectric paper strips 13 and Ik each comprised a pair of paper strips, one about 2.5 cm (1 inch) wide and 0.008 mm (0.3 thousandths of an inch) thick and the other about 2 thousandths of an inch wide .5 cm and a thickness of 0.009 mm (0.35 thousandths of an inch). The as yet unsealed capacitors of FIG. 2 were heated to 125 ° C. under vacuum for several hours. Thereafter, the Group 1 capacitors were filled with purified DOP and the Group 2 capacitors were filled with the same purified DOP that was used

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but 1 wt. of an epoxide had been added, which as diglycidyl ether of Bisphenol-A (Dow Epoxy No. 330) is known. The endurance test with these capacitors was as follows Get results:

Duration t
38O volts AC IQO ⁰ C

Failed capacitors after hours

Group 1 6 - 4200

Group 2 (epoxy) 0 - 4279

550 volts alternating current , 85 ⁰ C

Group 1 7-1130

Group 2 2 - 4205

From these results it can be seen that the failures are considerable reduced and the life of such capacitors containing the epoxy additive is extended. The first Endurance testing, the capacitors were tested under the harsh conditions of 100 ° C and 380 volts alternating current. Despite this Conditions, no failures occurred within 4279 hours of operation, while 6 of the capacitors that did not contain epoxy failed in 4200 hours. Under the even more stringent conditions of the second life test, the improved ones were Results equally surprising.

The noticeable advantage of adding epoxy to paper capacitors is worth mentioning. Normally, the well-known generation of water vapor by the paper and the well-known hydrolysis of ionizable products of the DOP ester appear to be incompatible. However, a very small amount of the epoxide appears to produce a more beneficial conversion than would be expected based on the stoichiometric proportions of the reactants.

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In the following example, capacitors of Figure 3, i.e. those containing polypropylene films 20 and 21 as dielectric, were used. subjected to similar test conditions.

Example 2

In this example, 2 groups of 10 unsealed capacitors each were assembled, as shown in FIGS. 1, 2 and 3. The dielectric consisted of biaxially oriented isotactic polypropylene strips about 48 mm (corresponding to 1 7/8 inch) wide and a thickness of about 0.009 mm (corresponding to 0.35 thousandths of an inch). The capacitors were dried in vacuo at room temperature and impregnated at room temperature. The capacitors of group 2 contained the same purified DOP, but 1 part by weight of diglycidyl ether of bisphenol-A had also been added. The capacitors were sealed after the vacuum drying and impregnation at room temperature and wärmegetrankt for two hours at 100 ⁰ C. The following results were obtained:

Capacity / power factor at 300 volts AC

and 85 ° C

DC dielectric strength in kilovolts per O _a O25 mm thickness of the poly-100 ⁰ C 85C propylene film ■ ·

Group Γ 3.52 / 0.39 3.58 / 0.34 5, ^ 9

Group 2 3.5 ^ / 0.28 3.60 / 0.26 5.57

The same capacitors were subjected to a life test, the following results were obtained:

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Lifetime test 300 volts alternating current 85 ⁰ C

Hours to failure

Group 1 after 256 hours remained 3

Capacitors

Group 2 (Epaxyd) after 256 hours remained 7

Capacitors

Example 3

In this example, the capacitors according to the invention were compared with known similar capacitors which contained chlorinated diphenyl as an impregnating agent to which about 0.3% by weight of epoxy had been added. 3 groups of 10 capacitors each were assembled according to the construction of FIG. The dielectric was composed of a polypropylene film of about 48 mm width and 0.009 mm thickness, as in Example 2. The capacitors were at room temperature in vacuum for several hours and then dried impregnated tei room temperature with the indicated impregnating agent, to which 1 wt -.% Diglycidylather of bisphenol -A had been added. Thereafter, composed from the capacitors and subjected them to a permanent Wärmetränkung H hours at 100 ⁰ C. life tests and measurements of the dielectric strength at a ramp rate of l80 volts DC per second at 85 ⁰ C are listed below:

Original number of failed Kon major chschlagfe- capacitors per number of gestißkeit tested capacitors 85 ⁰ C in kilovolts ^to

average at 300 volts at 550 volts

Alternating current alternating current

100 ⁰ C 85 ⁰ C

Group 1

purified 1.92 7 / 10-256 6 / 9-256

DOP without epoxy

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Original

Breakthrough

sturdiness

85 C in kilovolts

average

Number of failed capacitors per number of capacitors tested after hours

at 300 volts
Alternating current

100 ° C

at 550 volts AC

85 ⁰ C

Group 2

Purified 1.95 DOP with 1 % epoxy

Group 3

chlorinated 1 _} 76 diphenyl and epoxy

6 / 9-867 7 / 9-835 (first failure
after 39 ¹ J hours)

8 / 9-256 9 / 9-177

The above results show that the DOP stabilized in the inventive method passes the endurance test at high temperature better than the other capacitors. It should be noted that the first failure of a capacitor with DOP epoxy at 380 volts alternating current and 100 ^{° C. occurred after 39 1} hours of operation, while the non-stabilized DOP capacitors had 7 failures in 256 hours and in the case of the capacitors with chlorinated diphenyl as impregnation agent, 8 capacitors failed in 256 hours.

There have been assembled, further capacitors and treated with DOP containing up to 10 wt. ~% Of the diglycidyl ether of bisphenol-A. For example, a small capacitor having the structure of Figure 5, containing DOP as an impregnating agent and impregnated as described in US Pat. No. 3,363,156, has been assembled and good results have been obtained.

It can be seen from the above examples that the epoxy plays an important role in the life of the capacitor plays. The epoxy stabilizer according to the present invention is characterized in that it is in its special environment

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is able to work with such chemical elements or Connections to interact which are usually present in electrical capacitors or during operation generated to prevent these connections, dismantle the DOP. These elements and compounds are those that are created in a capacitor, the DOP as an impregnating agent and in the absence of any materials that could generate HCl. Most known epoxies, which are otherwise compatible with capacitors appear to give the desired result to varying degrees. In Both water and acids are present in the vicinity of the condenser or are formed. The esters can be cleaved with the formation of acids and alcohols. It is believed that the epoxy reacts with such acids, preventing the acid from degrading the ester or preventing the capacitor from failing to cause. The epoxy also seems to have problems with the hydro by combining with the water in the system. The epoxy also seems to passivate damage in the foil or to cover. In capacitors with a paper dielectric, the epoxy can stabilize the system with the Cellulose react. The function of the epoxy appears to be considerably different when only a film dielectric, i.e. H. there is no paper dielectric in the capacitor. One reason for this is that there are various materials in the film are, like stearates and antioxidants, that are not found in paper and it is also due to the low water content of the film. In this way, the stabilization of an ester-impregnated, Capacitor exclusively containing film as a dielectric can be achieved by means of a different mechanism, which however is not yet fully known at the moment.

While the function of the epoxy ultimately relates to an operating capacitor, it also plays one essential role in the ester in which it is dissolved. In this ester, the epoxy acts with the degradation products of the ester and

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thus alleviates the hydrolysis problem. The epoxy also combines with impurities in the ester, which the ester has to deal with before it is used in a condenser, e.g. during storage, the May be exposed to transport and handling.

The epoxy compound that can be used in the context of the present invention can generally be characterized by containing the following group:

CH CH

the z. B. in glycidyl ethers and derivatives of Ethylehoxyd is. Specific examples of these compounds are phenoxypropylene oxide (phenyl glycidyl ether), glycidyl allyl ether, Benzy1-ethylene oxide, styrene oxide, 1,3-bis (2,3-epoxy-propoxy) benzene and 4,4'-bis (2,3-epoxy-propoxy) diphenyldimethyl methane. aside from that Commercially available epoxides can still be used in the context of the present invention, such as that known under the name EP107 Di (2-ethylhexyl) -4,5-epoxy-tetrahydrophthalate, which is available under the name EP2O1 known 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexanecarboxylate and the 1-epoxyethyl-3,4-epoxycyclonexane known under the name EP2O6. if If desired, one can also use mixtures of two and more / epoxy compounds use. One or more of these epoxies are e.g. In U.S. Patents 3,362,908, 3,242,401, 3,242,402 and 3 170 986 by the applicant.

Tests have shown that the specific type of epoxy is not critical. Different epoxies or mixtures of Epoxies can be used so long as an effective amount thereof is added. How large this effective amount is depends primarily Line of the molecular weight, the reaction rate and

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the solubility in the impregnation agent. Epoxies with a higher molecular weight are to be used in larger amounts than those epoxides with a lower molecular weight. In general, amounts above 0.01 wt. and advantageously between about 0.01 and about 10 weight percent of the epoxy is useful. The epoxies act in a manner that is believed to be the same for all epoxies because of their chemical structure. Their response time and their effect are advantageous for the DOP in the capacitor. In the above examples, the main attention was paid to comparative results of DOP with and without the use of epoxies.

The epoxy can be introduced into the capacitor in a number of ways will. It can or can be incorporated into the polypropylene dielectric material during manufacture add it to the liquid DOP before or after inserting it into the capacitor case. Preferably that will Epoxy combined with the DOP as a solution and this solution is used to impregnate the capacitor. A main reason for this approach is that the esters, including DOP, are sensitive to elevated temperatures and that they are at can be subject to strong changes with increasing temperatures. The addition of the epoxy to the ester therefore pre-stabilizes it heating, especially during the impregnation process, the ester, not to mention the stabilization in the condenser.

DOP is compatible with both the polypropylene film dielectric alone and with paper. The preferred type of Impregnation is described in U.S. Patent '3,363,156, and it is referred to as essentially complete impregnation. A form of essentially complete impregnation includes the heating of the impregnated capacitor to an elevated temperature, preferably above 85 ° C via a

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It takes a long time to not only induce the DOP to penetrate the molecular structure of the polypropylene, but also to convert the polypropylene into a kind of semi-permeable membrane for the DOP and thus allow the DOP to penetrate the film. DOP penetrates the polypropylene film more slowly than chlorinated diphenyl. The best results were obtained when more intensive evacuation or drying was used. A 24-hour drying cycle, with temperatures of 130 to I ^{1 0} C IO has been successfully used, with the introduction of the DOP held in the capacitor at 100 ⁰ C.

Soaking can be continued as a specific cycle after the condenser has been impregnated and sealed, and it is an important criterion. The heat-soaking may be carried out at temperatures above 85 ⁰ C and preferably in the range of 100 - 120 ⁰ C take place. The best results were obtained with the larger and more difficult to impregnate capacitors when a variety of heat soaks were applied after impregnation. Thus, a first Wärmetränkung was carried out by ordering the capacitors in an oven and the temperature increased to about 110 ⁰ C. After 8 hours at this temperature, the capacitors were allowed to cool to about room temperature. The temperature of the furnace was then increased to 110 ^° C. and this temperature was maintained for a further 8 hours. Comparative tests have shown that the described multiple hot drinks leads to better results than a single hot drink carried out over 16 hours. A preferred process for making DOP-impregnated capacitors using paper includes drying under vacuum at about 120 to 140 ° C, then impregnating at above 100 ° C and then soaking several times as described. If only films are used as the dielectric, drying can be carried out at lower temperatures and for shorter times.

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7341356

The polypropylene film as disclosed in U.S. Patent 3,363,156 is a stereoregular crystalline, biaxially oriented film, which is also within the scope of the present invention preferred "and was used in all examples. Under crystalline is to be understood as meaning that the material had a considerable crystalline content and the crystallinity the physical properties of the material determined. The use of DOP is not limited to the listed dielectrics and there can be other members of the polyolefin group as well as other synthetic resins such as polycarbonate, polysulfone and polyester can be used as dielectrics. The significant feature is the use of the DOP together with an epoxy stabilizer.

The stabilized impregnation agent according to the present invention, particularly DOP, is an improved impregnation agent for such capacitors which are exposed to high voltage loads and high temperatures. A high voltage load for the dielectric, when it is a film of a synthetic resin such as polypropylene, is from about 750 volts per 0.025 mm (equivalent to 1/1000 of an inch) thickness of the polypropylene up to 1200 volts per 0.025 mm, the more critical Part of the high load is in a range starting at about 900 volts per 0.025 mm and extending up to about I ¹ JOO volts per 0.025 mm. In addition, capacitors exposed to such stresses are impregnated in a manner which is described in US Pat. B. brings a high corona starting voltage with it, which is related to the thickness of the dielectric. In high voltage power capacitors for shunt applications where the total thickness of the dielectric between the electrodes can be on the order of 0.025 mm, the Oorona starting voltage at room temperature must generally be above 2000 volts

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and in many cases it must be greater than 2500 volts. For applications at low voltages, where thinner dielectrics are used, the corona start voltage can be lower. The corona starting voltage is usually 1 1/2 to 2 1/2 times the highest voltage load in the dielectric the application voltage of the capacitor at room temperature and it is stable under variable condenser operating conditions.

DOP is useful for many different types of dielectric systems with a single dielectric material, such as paper only, film only, or mixtures thereof. An example of a mixed system is shown dielectric k in the arrangement of the figure in which a sheet of paper 13 is adjacent to the one electrode. 11 It can be seen from the embodiment of Figure 5 that other mixed dielectrics comprise two films 20 and 21 with a sheet of paper 13 therebetween, or, conversely, that two sheets of paper are used with a film therebetween.

Figure 6 shows a high voltage phase advancing capacitor which requires a low power factor. The capacitor 22 comprises a large container 23 with a volume of approximately 23 (corresponding to 0.8 US feet ) _t in which a large number (10-40) of elongated coils 10 are arranged. These wraps 10 can be about 25-64 cm (10-25 inches) in length. To be effective, the DOP impregnant and additive must have penetrated through each roll 10, since failure of only one roll 10 will cause failure of the entire capacitor. Therefore, these power capacitors 22 are subjected to exceptional drying conditions, e.g. B. they are exposed to ^{temperatures of 100 to 150 0} C at a pressure of about 200 u mercury for 15 to 30 hours. While they are still under vacuum and at an elevated temperature, they are usually filled with the impregnating agent

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. ^. 2341358 to

is the impregnating agent when pouring into the housing also "at a temperature of about 70 - 80 ° C then the capacitor is usually sealed and again elevated temperatures of about 80 -. exposed to 120 ⁰ C for extended times of the size of the capacitor and the type of dielectric material used depend on all paper capacitors require a minimum time, not However, a subsequent heating All Pilm capacitors to a heat soaking for 16 -.. require 2k hours.

example k

Investigations have been made with other aromatic esters as impregnating agents that contain epoxy additives. Such a test was carried out with typical capacitors, as in the examples above, in which the dielectric was polypropylene and dicaprylphfchalate was used as the impregnating agent. The epoxy was EP2O6 and was in an amount of 1 wt - used.%. These capacitors were tested at 550 volts AC and 85 ° C with an extremely high film load of 1570 volts per 0.025 mm of polypropylene thickness, surprisingly, after 9500 hours of operation, these capacitors still worked just as well as control capacitors that used chlorinated diphenyl as the impregnation agent.

Example 5

Capacitors with the configuration according to FIGS. 12 and 5 were manufactured. The dielectric consisted of a strip of paper about 0.012 mm (0.5 / 1000 inch) thick and having a width. of about 92 mm (3.625 inches) and 2 strips of about 0.017 mm (0.7 / 1000 inch) thick polypropylene film of equal width. The capacity was about 0.5 ^ uf. The capacitors were 24 hours under vacuum at 130 - 140 ⁰ C impregnated and then dried at 100 ° C. Two groups of capacitors were examined. One group contained DOP as an impregnating agent with 1 wt. Ί epoxy and the other group used 80 wt. DOP and 20 wt -.% Dodecylbenzene. To this mixture one added

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i \

1 wt -.% Of the epoxy EP2O6. Thereafter the capacitors were sealed and heat for 8 hours at 100 ⁰ C ge .. The impregnated capacitors were subjected to a corona starting voltage test and heat soaked for a further 8 hours. A corona starting voltage test was then carried out on the capacitors. There was a sharp increase in the corona starting voltage. I. E. the corona starting voltage was noticeably increased by the second heat soaking process, which was necessary to bring the capacitor to a satisfactory level of the corona starting voltage and which was higher for the impregnating agent made of DOP and dodecylbenzene than for the DOP as impregnating agent alone.

Not all dielectric fluids are satisfactory as impregnating agents for capacitors. A dielectric liquid should have the following general properties; it should be in a cleaned or cleanable form, have a boiling point and freezing point outside the operating temperatures of the condenser and a flash point above 175 ° C. Darüberjhinaus the liquid should have a vapor pressure below atmospheric pressure at temperatures up to 200 ⁰ C and preferably up to 300 ⁰ C and a dielectric constant higher than 2, in particular in synthetic film dielectrics, such as polypropylene, and preferably 4 and more on paper dielectrics . In addition, the liquid should have a relatively low viscosity, namely liquid remain less than 1000 centistokes at 25 ° C and up to -40 ⁰ C.

The power factor or dissipation factor is an extremely important criterion for a capacitor, especially for an AC phase shift capacitor, since it usually operates at elevated temperatures, and such temperatures normally exposed during manufacture. The power factor increases rapidly with the temperature. The power factor of the cleaned Impregnant itself should be considerably less than

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10 % and preferably less than 5% » measured at 100 ° C and 100 Hz so that the power factor in the capacitor can be reduced to less than about 1%. This low power factor must be maintained for long lifetimes extending up to several years.

In addition, the impregnant should be compatible with the other materials of the capacitor and it should be can withstand changing operating temperatures at high voltage loads. Easy handling, impregnation and other physical properties are desirable. In addition, it is very desirable that the impregnation agent be light is biodegradable compared to chlorinated diphenyls and has a low level of toxicity.

The most suitable for the purposes of the present invention aromatic esters meet the criteria mentioned and are therefore preferred in the context of the present invention. Preferred Esters which otherwise meet suitable dielectric tests are the reaction product of an aromatic acid with an alcohol. A typical compound has the following formula:

R Γ - C - 0-0

where R is, for example, the aromatic substituent or radical of pyromellitic acid, terephthalic acid, phthalic acid, trimellitic acid, trimesic acid or one of the groups phenyl, naphthyl, bisphenyl, ToIyI, etc., X can represent an integer from 1 to 4 and where R ^{1 is} an alkyl or ary group, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc. Des are straight-chain alkyl groups.

However, branched alkyl groups can also be used, for example 2-ethylhexyl, isopropyl, isobutyl, isooctyl, etc. Examples of aromatic esters of phthalic acid which are useful in the context of the present invention include dimethyl, Diethyl, dipropyl esters, etc. An example of an ester

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the Be nzoeß ^ ¹¹¹ "® ^is butyl benzoate.

In addition to the esters of organic acids, the reaction products other acids, especially phosphoric acid, can be used with the alcohols mentioned above. Specific examples include tri-cresyl phosphate and tri-phenyl phosphate. they are They are also amenable to degradation by hydrolysis or oxidation and therefore the presence of the epoxides has an advantageous effect on them too the end. The aromatic esters are In the present invention unique in that the reaction properties are predictably similar, especially for the phthalate ester, so if the other Component, if any, is otherwise a good condenser impregnant, the combination of the aromatic Esters and epoxy Is useful.

The esters of the present invention can contain mixtures of esters or mixtures of esters and others, otherwise satisfactory include lapregnants. It is most preferred that the impregnating agents used contain the ester of present invention as a main ingredient. Pure the For purposes of the present invention, a mixture may comprise mixtures of esters according to the present invention, for example DOP and bibutyl phthalate as well as DOP and didodecyl phthalate. The mixture can also contain an ester according to the present invention together with an aliphatic ester such as dibutyl sebacate or castor oil. Further, the mixture can contain the ester of the present invention and a hydrocarbon in general, such as a mineral oil, alkyl naphthalenes, polybutenes and the like include. Specific examples of these mixtures are DOP and mineral oil and DOP and dodecylbenzene. The mixes can too other esters such as phosphates, e.g., tricresyl phosphate and triphenyl phosphate include. The mixtures are used to provide the impregnant with properties similar to those of the esters according to the present invention are different, such as an increased dielectric constant. The added material

409809 / 097S

can also be in the form of a diluent or an impregnation aid, z. B. a wetting agent can be used. An example of a material that has a variety of punctures fulfilled, is dodecylbenzene, which acts as a wetting agent and as an impregnating agent and can therefore be used in relatively large quantities. While it is preferred that the ester be after of the present invention dominates the mixture as far as the electrical properties are concerned, it is also in the

η of the present invention that lesser amounts of the ester of the present invention can be used. So can 10 to hO wt. of the ester of the present invention can be added to other impregnating agents to change their properties. In the context of mixtures in the present invention, the mixture can comprise large amounts of a suitable epoxy, the epoxy serving both punctures, ie, to be a stabilizer and an impregnating agent.

The invention is specific with aromatic esters as described which show the most improved results. An aromatic ester stabilized with epoxy, such as DOP, gives a waterproofing agent that is unexpectedly the same, or in some cases, better than currently best waterproofing agent, chlorinated diphenyl.

40980 9/0976

Claims (1)

χ * Claims Dielectric liquid impregnation agent for use in electrical equipment, labeled by a liquid aromatic ester, the one Epoxy material has been added which is associated with adverse contaminants present in electrical devices or can be generated during operation, can interact to break down the aromatic ester to avoid. 2. Impregnation agent according to claim 1, characterized in that it is the main component, an ester of the formula - C - 0 - R contains, wherein R is an aromatic substituent, R ^{1 is} an alkyl or aryl group and X is an integer from 1 to H in which a stabilizer is dissolved which is characterized by the following group - CH CH 3. Impregnation agent according to claim 2, characterized in that the aromatic ester is a Is an ester of phthalic acid with an alcohol. 4. Impregnation agent according to claim 3, characterized characterized in that the phthalic acid ester is an ester of 2-ethylhexyl alcohol. 409809/0976 5. Impregnation agent according to claim 2, d a du r c h It indicates that the ester is selected from dimethyl phthalate, diethyl phthalate, dipropyl phthalate, dibutyl phthalate, Diallyl phthalate, dihexyl phthalate, diheptyl phthalate, Dioctyl phthalate, dinonyl phthalate, didecyl phthalate, dicapryl phthalate, an ester of benzene acid with an alcohol, an ester of an aromatic alcohol which is a phosphoric acid contains or tricresyl phosphate. 6. Impregnation agent according to claims 1-5, characterized in that the epoxy is present in an amount greater than about 0.01 weight percent. 7. Impregnating agent according to claim 6, characterized in that the epoxy in an amount of about 0.01 to about 10 percent - is present.%. 8. Impregnation agent according to claims 1-7, characterized in that the epoxy stabilizer is a derivative of ethylene oxide. 9. Impregnation agent according to claims 1-8, characterized in that the epoxy is a Is a derivative of glycidyl ether. 10. Impregnation agent according to claims 1-9, characterized in that the epoxy is bisphenol-A diglycidyl ether. 11. Impregnation agent according to claims 2-10, characterized in that the liquid The composition contains the ester in a mixture, the ester in the mixture in the dielectric device as an impregnating agent works. 403809/0376 7341356 12. Impregnation agent according to claim 11, characterized in that the mixture is an ester and includes a hydrocarbon. 13. Impregnation agent according to claim 12, characterized in that the hydrocarbon is an alkyl benzene. Ik. Impregnating agent according to Claim 2, characterized in that it comprises a liquid aromatic ester of 2-ethylhexyl alcohol to which a derivative of slyeidyl ether has been added in an amount of about 0.01 to 10% by weight as a steel agent. 15. Impregnation agent according to claim 14, characterized characterized in that the ester is dioctyl phthalate and the epoxy is a diglycidyl ether of bisphenol A. 16. Long life capacitor with a sealed case , at least one capacitor winding in the housing, wherein the capacitor coil comprises a pair of electrodes and a dielectric material therebetween and a non-halogenated one Impregnating agent is present in the housing and impregnates the capacitor winding,. through this characterized in that the impregnation agent comprises a liquid aromatic ester and an epoxy additive, the bit impurities that are present in the capacitor or that may be generated during its operation, can interact to the electrical deterioration to avoid the capacitor. 17 · Capacitor according to claim 16, characterized in that that the additive is a liquid epoxy of high molecular weight and low volatility. 409809/0376 - in - ι * 18. Capacitor according to claims 16 and 17 »thereby characterized in that the aromatic ester is a phthalic acid ester. 19. Capacitor according to claim 18, characterized in that that the aromatic ester is an ester of 2-ethylhexyl alcohol. 20. Capacitor according to claims 16-19, characterized in that the epoxy is a diglycidyl ether of bisphenol-A. 21. A capacitor according to claim 20, characterized in that the epoxy in an amount of more than 0.01 wt -.%, And is preferably present in an amount between 0.01 and about 10 Gfew.- £. 22. Capacitor according to claims 16-21, characterized in that a paper dielectric is at least a portion of the dielectric material. 23. Capacitor according to claims 16-21, characterized in that a synthetic resin is at least part of the dielectric. 2h. A capacitor according to Claim 23, characterized in that the synthetic resin is polypropylene. 25. Capacitor according to claims 16-21, characterized in that the dielectric comprises a mixed dielectric of polypropylene and paper. 2o. Capacitor according to Claim 24, characterized in / at an AC voltage load of the polypropylene at the application voltage of the capacitor 409809/0976 7341356 from about 750 to more than 1200 volts per 0.025 mm (1/1000 of an inch) thickness of the polypropylene the capacitor. has a low power factor of less than about 1% when measured at room temperature for long life. 27. Capacitor according to claim 26, characterized in that that the capacitor is at a voltage load of more than 900 volts per 0.025 mm of polypropylene has a power factor of less than 0.5 Κ. 28. Capacitor according to claims 23 and 24, characterized gekennzei chnet that the pair of electrodes have a metallized surface on the strip of synthetic Resin includes. 29. A method for producing a capacitor according to claim l6, characterized in that one a) the housing and the coil evacuated and heated to remove moisture, b) fills the housing with the impregnation agent, c) heating the housing to an elevated temperature long enough to cause substantially complete impregnation of the dielectric, d) brings the condenser to room temperature and e) seals the housing before or after step (c). 30. A method for impregnating an electrical capacitor according to claim l6, with an aromatic ester impregnating agent, characterized by the following levels: a) placing the capacitor in a housing, b) heating the capacitor to a temperature under vacuum from about 100 to 110 ° C for at least about 8 hours, c) Pulling the housing under, r vacuum and at elevated temperature with an ester impregnation agent in which one 403809/0976 ίο Epoxy compound in an amount of more than 0.01 wt -%, and is dissolved. d) soaking the catalyst for at least 4 hours a temperature of 85 to 140 ° C in order to obtain an essentially complete impregnation. 31. The method according to claim 30, characterized in that the capacitor contains paper in its dielectric system, and that the heating according to step (b) is carried out for at least 2k hours. 32. The method according to claims 29 and 30, thereby characterized in that the condenser is cooled after the heat soaks and the heat soaks are repeated thereafter will. 33. The method according to claims 30 and 31 »characterized in that the impregnation agent used from an aromatic ester by means of a column purification process with removal substantially cleans all foreign materials, one adds to the aromatic ester at least 1 Gew.-Jf of an epoxy to this to dissolve in the aromatic ester and then impregnate the capacitor according to claim 30. 409809/0976